Internal combustion engines mix ingested air with fuel to form a combustion mixture. The combustion mixture is compressed and is combusted within a cylinder to reciprocally drive a piston, thereby generating drive torque. The mass of air and fuel within the combustion mixture effects engine torque output and emissions.
An engine system's volumetric efficiency refers to the actual volume of air that is ingested by a cylinder as compared to the theoretical volume of air that could be ingested. For example, an engine system with an 80% volumetric efficiency is only ingesting 80% of the air volume that it theoretically could ingest. Engine systems that operate with volumetric efficiencies lower than 100% produce less maximum torque than they are theoretically capable of producing. However engines are not limited to 100% volumetric efficiency with proper induction tuning
Traditionally, increased volumetric efficiencies (e.g., greater than 90%) over a wide speed range have been achieved by adding components to the induction system. For example, some engine systems implement an additional valve within the intake runner, which is selectively opened and closed to produce an air ramming effect at engine cycle frequencies away from the natural frequency of the induction system. Although increases in volumetric efficiency can be achieved, increased cost and complexity are associated with such engine systems. Other traditional engine systems either also include additional components and/or are able to achieve volumetric efficiency higher than 90% over only a limited engine speed range.